Liquid crystal projector apparatus and driving method for liquid crystal projector apparatus

ABSTRACT

The present invention provides a liquid crystal projector apparatus and a driving method for a liquid crystal projector apparatus, which can display an image with an optimum picture quality free from an influence of a temperature variation of a liquid crystal panel without the necessity to directly measure the temperature of the liquid crystal panel. The liquid crystal projector apparatus includes a temperature sensor for detecting a temperature at a location in the liquid crystal projector apparatus except liquid crystal panels, a memory for storing temperature detection data obtained by the temperature sensor within a period from a power supply starting time to a steady operation entering time of the liquid crystal projector apparatus, arithmetic operation means for estimating a temperature of each of the liquid crystal panels based on the temperature detection data stored in the memory to indirectly obtain the temperatures of the liquid crystal panels, and liquid crystal drive sections for correcting drive voltages for driving the liquid crystal panels with output signals of the arithmetic operation means and applying the corrected drive voltages to the liquid crystal panels.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a liquid crystal projector apparatuswhich includes a liquid crystal display panel for optically modulatinglight from a light source with an input signal and projects theoptically modulated light from the liquid crystal panel to display animage and a driving method for a liquid crystal projector apparatus.

[0002] As an example of an image display apparatus, a liquid crystalprojector apparatus which makes use of a liquid crystal panel is known.Such liquid crystal projector apparatus include an apparatus called rearprojector.

[0003] A liquid crystal projector apparatus of the type mentioned usesthree liquid crystal panels (also called liquid crystal light valves)for optically modulating the colors of, for example, red, green and blueto combine light of the three components and projects the combined coloronto a screen through a lens to display a color image in an enlargedscale. A liquid crystal projector apparatus of the type describedincludes a lamp as a light source for projecting a video (image) todisplay it. The lamp generates a great amount of heat and requirescooling thereof.

[0004] By the way, liquid crystal panels used in a liquid crystalprojector apparatus have such a so-called V-T characteristic (drivevoltage-transmissivity) as illustrated in FIG. 18. The axis of ordinateof the V-T characteristic indicates the transmissivity of a liquidcrystal panel, and the axis of abscissa indicates the driving voltage(applied voltage) applied to the liquid crystal panel. The V-Tcharacteristic has a characteristic that it is shifted in the directionof the axis of abscissa in response to a variation of the temperature.

[0005] The V-T characteristic has a characteristic that, if thetemperature rises, for example, from 26.5° C. to 48.6° C. and the V-Tcharacteristic is shifted, then in a gradation portion of the drivingvoltage of 2.5 V, a drop of the transmissivity of approximately 20%,that is, a drop of the luminance, occurs. Such a variation of theluminance by a temperature variation as just described exhibits itsmaximum with an intermediate gradation.

[0006] Such a drop of the transmissivity of a liquid crystal panel, thatis, a drop of the luminance of a liquid crystal panel, as describedabove is caused by such a shift of the V-T characteristic as shown inFIG. 18 by the temperature of the liquid crystal panel. Therefore, thevariation of the luminance of the liquid crystal is not uniform amongdifferent gradations. In other words, if a drive signal portion iscorrected with a gain or an offset as in correction of the brightness inan ordinary television receiver or the like, then the gradation propertyof the liquid crystal panel is disordered.

[0007] Therefore, for the correction against a temperature variation ofa liquid crystal panel, not correction of the brightness but correctionof the shift of the V-T characteristic diagram must be performed, and itis known by Japanese Patent No. 2924073 that a shift of a drive voltage(applied voltage) to a liquid crystal panel, that is, a shift of the V-Tcharacteristic, with regard to the axis of abscissa is required.

[0008] By the way, where a liquid crystal projector apparatus is used,upon starting of a power supply, the temperature of the liquid crystalpanels corresponds to a room temperature. However, after starting of thepower supply, since the liquid crystal panels are heated by a lightsource such as a lamp, the temperature of the liquid crystal panelsrises up to approximately 50° C.

[0009] The liquid crystal panels are disposed in a housing of the liquidcrystal projector apparatus, and the liquid crystal panels are cooled bya cooling fan in the housing. In a liquid crystal projector apparatus ofthe structure that the liquid crystal panels are cooled by a flow ofwind by a cooling fan in this manner, the air in the housing iscirculated to cool the liquid crystal panels without taking in externalair. The reason why the liquid crystal panels are cooled by aircirculation in the housing without taking in external air in this manneris that it is intended to augment the dust-proof performance. In aliquid crystal projector apparatus of such a structure as justdescribed, a fixed time requires until the temperature of the liquidcrystal panels rises.

[0010] In order to directly measure the temperature of a liquid crystalpanel, it is necessary to provide a temperature sensor in a closelycontacting relationship with the liquid crystal panel positioned in thedust-proof housing. However, to provide a temperature sensor in aclosely contacting relationship with a liquid crystal panel in thismanner is difficult due to the following reason in terms of thestructure.

[0011] As the reason, there is a problem that the temperature sensorcannot be provided at a position at which light of the liquid crystalpanel passes, that the area of a portion of each liquid crystal panel atwhich the temperature sensor is provided is limited because the liquidcrystal panels are small in size, that, where the temperature sensor isbuilt in the liquid crystal sensor, an increased cost is required, orthe like.

[0012] Therefore, it is a possible idea to dispose the temperaturesensor at a location in the housing other than the liquid crystalpanels, for example, on a circuit board in the housing. Where thetemperature sensor is disposed on the circuit board in this manner, adifference appears between temperature rise curves of the actualtemperature of the liquid crystal panel and the temperature detected bythe temperature sensor on the circuit board.

[0013] Where it is intended to indirectly measure the temperature of theliquid crystal panel by means of the temperature sensor provided on thecircuit board, since a difference appears between the temperature in theapparatus and the actual temperature of the liquid crystal panel, evenif it is tried to measure the actual temperature of the liquid crystalpanel, an error occurs. Accordingly, if, when a power supply for theliquid projector apparatus is started, it is tried to indirectly measurethe temperature of the liquid crystal panel by means of the temperaturesensor on the circuit board and correct the value of the driving voltageto be applied to the liquid crystal panel, then an error occurs.

[0014] Usually, in an environment wherein a television receiver in whicha Braun tube or the like is used is watched, the room temperaturevariation during use of the television receiver is, where the roomtemperature is 25° C., approximately ±10° C. with respect to thetemperature of 25° C. However, when a liquid crystal projector apparatusis used, where the room temperature is 25° C., the temperature variationof the liquid crystal panel upon starting of the power supply is a riseof more than 25° C. with respect to 25° C. (50° C.−25° C.=25° C.). Ifthe time of the temperature variation of the liquid crystal panel whenthe power supply is started is shorter than the time in which theluminance of the light source in the form of a lamp is stabilized, thenthe temperature of the liquid crystal panel rises in a moment.Accordingly, no particular problem occurs because the user can adjustthe picture quality to a stable optimum picture quality while the userdoes not become aware that the temperature variation of the liquidcrystal panel when the power supply is started has an influence on theprojected picture quality.

[0015] In the liquid crystal projector apparatus, however, since theliquid crystal panels are cooled by circulated air in the housing asdescribed above, the rate of the temperature rise of the liquid crystalpanels upon starting of the power supply is lowered by such cooling bythe cooling fan when compared with that in an alternative case whereinthe liquid crystal panel is not cooled. Consequently, since the rise ofthe temperature variation of the liquid crystal panel when the powersupply is started is slow, a drop of the luminance of the liquid crystalpanel occurs, and this gives rise to a problem of at what point of timethe picture quality should be adjusted to an optimum picture quality.Since particularly a liquid crystal panel for a liquid crystal projectorapparatus wherein air is circulated in the housing as a countermeasurefor dust-proof as described above requires a longer period of time untilthe temperature of the liquid crystal panel rises upon starting of thepower supply, a longer period of time is required until the temperatureof the liquid crystal panel upon steady operation is stabilized afterstarting of the power supply, and a variation of the picture quality bya temperature variation of the liquid crystal panel when the powersupply is started becomes liable to be visually recognized by the user.

SUMMARY OF THE INVENTION

[0016] It is an object of the present invention to provide a liquidcrystal projector apparatus and a driving method for a liquid crystalprojector apparatus which eliminate the subjects described above and candisplay an image with an optimum picture quality free from an influenceof a temperature variation of a liquid crystal panel without thenecessity to directly measure the temperature of the liquid crystalpanel.

[0017] The invention of claim 1 is a liquid crystal projector apparatuswhich includes a liquid crystal panel for optically modulating lightfrom a light source with an input signal and projects the opticallymodulated light from the liquid crystal panel to display an image,characterized in that it includes a temperature sensor for detecting atemperature at a location in the liquid crystal projector apparatusexcept the liquid crystal panel, a memory for storing temperaturedetection data obtained by the temperature sensor within a period from apower supply starting time to a steady operation entering time of theliquid crystal projector apparatus, arithmetic operation means forestimating a temperature of the liquid crystal panel based on thetemperature detection data stored in the memory to indirectly obtain thetemperature of the liquid crystal panel, and a liquid crystal drivesection for correcting a drive voltage for driving the liquid crystalpanel with an output signal of the arithmetic operation means andapplying the corrected drive voltage to the liquid crystal panel.

[0018] In claim 1, the temperature sensor detects a temperature at alocation in the liquid crystal projector apparatus except the liquidcrystal panel.

[0019] The memory stores temperature detection data obtained by thetemperature sensor within a period from a power supply starting time toa steady operation entering time of the liquid crystal projectorapparatus.

[0020] The arithmetic operation means estimates a temperature of theliquid crystal panel based on the temperature detection data stored inthe memory to indirectly obtain the temperature of the liquid crystalpanel.

[0021] The liquid crystal drive section corrects a drive voltage fordriving the liquid crystal panel with an output signal of the arithmeticoperation means and applies the corrected drive voltage to the liquidcrystal panel.

[0022] Consequently, although the actual temperature of the liquidcrystal panel is not measured directly by means of the temperaturesensor, the temperature of the liquid crystal panel is estimated basedon the temperature detection data obtained by the temperature sensor toindirectly obtain the temperature of the liquid crystal panel. And, theliquid crystal drive section corrects the drive voltage to be applied tothe liquid crystal panel corresponding to the temperature of the liquidcrystal panel with the output signal of the arithmetic operation means.Consequently, even if a long period of time is required for a rise ofthe temperature of the liquid crystal within the period of time afterthe power supply starting time till the steady operation entering timeof the liquid crystal panel, the temperature variation of the liquidcrystal panel does not have an influence on the picture quality, and animage can be displayed with an optimum picture quality.

[0023] According to the invention of claim 2, the liquid crystalprojector apparatus according to claim 1 is configured such that theliquid crystal drive section controls a dc component of the drivevoltage to be applied to the liquid crystal panel to correct thevoltage.

[0024] According to the invention of claim 3, the liquid crystalprojector apparatus according to claim 2 is configured such that thelight source and the liquid crystal panel are disposed in a housing, andthe liquid crystal projector apparatus further includes cooling meansfor circulating air in the housing without taking in external air tocool the liquid crystal panel in the housing.

[0025] In claim 3, where air is circulated in the housing without takingin external air to cool the liquid crystal panel in the housing, even ifa long period of time is required for a rise of the temperature of theliquid crystal panel, an image can be displayed with an optimum picturequality.

[0026] According to the invention of claim 4, the liquid crystalprojector apparatus according to claim 3 is configured such that theliquid crystal panel includes a liquid crystal panel for red, a liquidcrystal panel for green and a liquid crystal panel for blue, and theliquid crystal drive section includes a first liquid crystal drivesection for correcting a drive voltage for driving the liquid crystalpanel for red with an output signal of the arithmetic operation meansand applying the corrected drive voltage to the liquid crystal panel forred, a second liquid crystal drive section for correcting a drivevoltage for driving the liquid crystal panel for green with anotheroutput signal of the arithmetic operation means and applying thecorrected drive voltage to the liquid crystal panel for green, and athird liquid crystal drive section for correcting a drive voltage fordriving the liquid crystal panel for blue with a further output signalof the arithmetic operation means and applying the corrected drivevoltage to the liquid crystal panel for blue.

[0027] In claim 4, the liquid crystal panel for red, liquid crystalpanel for green and liquid crystal panel for blue can be used to displaya color image of an optimum picture quality.

[0028] According to the invention of claim 5, the liquid crystalprojector apparatus according to claim 1 is configured such that itfurther includes a room temperature detection sensor for detecting aroom temperature separately from the temperature sensor, and thearithmetic operation means arithmetically operates, at the power supplystarting time, a difference between the temperature detection data ofthe temperature sensor and room temperature detection data of the roomtemperature detection sensor.

[0029] In claim 5, the room temperature detection sensor for detecting aroom temperature is provided separately from the temperature sensor, andthe arithmetic operation means arithmetically operates, at the powersupply starting time, a difference between the temperature detectiondata of the temperature sensor and room temperature detection data ofthe room temperature detection sensor. Consequently, at the power supplystarting time, it can be discriminated whether the power supply startingis the first time starting or re-starting is performed after thestarting is stopped after power supply starting.

[0030] Consequently, since the temperature of the liquid crystal panelexhibits a rise, an error occurs with the estimated value of thetemperature of the liquid crystal panel within the period of time afterthe power supply starting time till the steady operation entering time,and consequently, the temperature of the liquid crystal panel can beestimated more accurately by discriminating whether or not re-startingis performed and an image can be displayed with a more optimum picturequality.

[0031] The invention of claim 6 is a driving method for a liquid crystalprojector apparatus which includes a liquid crystal panel for opticallymodulating light from a light source with an input signal and projectsthe optically modulated light from the liquid crystal panel to displayan image, characterized in that it includes a temperature detection stepof detecting a temperature at a location in the liquid crystal projectorapparatus except the liquid crystal panel by means of a temperaturedetector, an arithmetic operation step of storing temperature detectiondata obtained by the temperature sensor within a period from a powersupply starting time to a steady operation entering time of the liquidcrystal projector apparatus into a memory and estimating a temperatureof the liquid crystal panel based on the temperature detection datastored in the memory to indirectly obtain the temperature of the liquidcrystal panel by means of arithmetic operation means, and a drivevoltage supplying step of correcting a drive voltage for driving theliquid crystal panel with an output signal of the arithmetic operationmeans and applying the corrected drive voltage to the liquid crystalpanel.

[0032] In claim 6, the temperature detection step detects a temperatureat a location in the liquid crystal projector apparatus except theliquid crystal panel by means of a temperature detector.

[0033] The arithmetic operation step stores temperature detection dataobtained by the temperature sensor within a period from a power supplystarting time to a steady operation entering time of the liquid crystalprojector apparatus into a memory and estimates a temperature of theliquid crystal panel based on the temperature detection data stored inthe memory to indirectly obtain the temperature of the liquid crystalpanel by means of arithmetic operation means.

[0034] The drive voltage supplying step corrects a drive voltage fordriving the liquid crystal panel with an output signal of the arithmeticoperation means and applies the corrected drive voltage to the liquidcrystal panel.

[0035] Consequently, although the actual temperature of the liquidcrystal panel is not measured directly by means of the temperaturesensor, the temperature of the liquid crystal panel is estimated basedon the temperature detection data obtained by the temperature sensor toindirectly obtain the temperature of the liquid crystal panel. And, theliquid crystal drive section corrects the drive voltage to be applied tothe liquid crystal panel corresponding to the temperature of the liquidcrystal panel with the output signal of the arithmetic operation means.Consequently, even if a long period of time is required for a rise ofthe temperature of the liquid crystal within the period of time afterthe power supply starting time till the steady operation entering timeof the liquid crystal panel, the temperature variation of the liquidcrystal panel does not have an influence on the picture quality, and animage can be displayed with an optimum picture quality.

[0036] According to the invention of claim 7, the driving method for aliquid crystal projector apparatus according to claim 6 is configuredsuch that the liquid crystal drive section controls a dc component ofthe drive voltage to be applied to the liquid crystal panel to correctthe voltage.

[0037] According to the invention of claim 8, the driving method for aliquid crystal projector apparatus according to claim 7, wherein thelight source and the liquid crystal panel are disposed in a housing, andcooling means circulates air in the housing without taking in externalair to cool the liquid crystal panel in the housing.

[0038] In claim 8, where air is circulated in the housing without takingin external air to cool the liquid crystal panel in the housing, even ifa long period of time is required for a rise of the temperature of theliquid crystal panel, an image can be displayed with an optimum picturequality.

[0039] According to the invention of claim 9, the driving method for aliquid crystal projector apparatus according to claim 8 is configuredsuch that the liquid crystal panel includes a liquid crystal panel forred, a liquid crystal panel for green and a liquid crystal panel forblue, and a first liquid crystal drive section corrects a drive voltagefor driving the liquid crystal panel for red with an output signal ofthe arithmetic operation means and applies the corrected drive voltageto the liquid crystal panel for red, a second liquid crystal drivesection corrects a drive voltage for driving the liquid crystal panelfor green with another output signal of the arithmetic operation meansand applies the corrected drive voltage to the liquid crystal panel forgreen, and a third liquid crystal drive section corrects a drive voltagefor driving the liquid crystal panel for blue with a further outputsignal of the arithmetic operation means and applies the corrected drivevoltage to the liquid crystal panel for blue.

[0040] In claim 9, the liquid crystal panel for red, liquid crystalpanel for green and liquid crystal panel for blue can be used to displaya color image of an optimum picture quality.

[0041] According to the invention of claim 10, the driving method for aliquid crystal projector apparatus according to claim 6 is configuredsuch that the liquid crystal projector apparatus further includes a roomtemperature detection sensor for detecting a room temperature separatelyfrom the temperature sensor, and the arithmetic operation meansarithmetically operates, at the power supply starting time, a differencebetween the temperature detection data of the temperature sensor androom temperature detection data of the room temperature detectionsensor.

[0042] In claim 10, the room temperature detection sensor for detectinga room temperature is provided separately from the temperature sensor,and the arithmetic operation means arithmetically operates, at the powersupply starting time, a difference between the temperature detectiondata of the temperature sensor and room temperature detection data ofthe room temperature detection sensor. Consequently, at the power supplystarting time, it can be discriminated whether the power supply startingis the first time starting or re-starting is performed after thestarting is stopped after power supply starting.

[0043] Consequently, since the temperature of the liquid crystal panelexhibits a rise, an error occurs with the estimated value of thetemperature of the liquid crystal panel within the period of time afterthe power supply starting time till the steady operation entering time,and consequently, the temperature of the liquid crystal panel can beestimated more accurately by discriminating whether or not re-startingis performed and an image can be displayed with a more optimum picturequality.

[0044] As described above, according to the present invention, an imagecan be displayed with an optimum picture quality free from an influenceof a temperature variation without the necessity to directly measure thetemperature of a liquid crystal panel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045]FIG. 1 is a perspective view of a preferred embodiment of a liquidcrystal projector apparatus of the present invention.

[0046]FIG. 2 is a front view showing an example of the liquid crystalprojector apparatus of FIG. 1.

[0047]FIG. 3 is a view showing an example of a structure of a coolingsystem for a light source of the liquid crystal projector apparatus ofFIG. 1.

[0048]FIG. 4 is a perspective view showing an example of a structure ofan optical unit of the liquid crystal projector apparatus.

[0049]FIG. 5 is a view showing an example of an internal structure ofthe optical unit.

[0050]FIG. 6 is a view illustrating an example of circulation of air forcooling a liquid crystal panel in a housing of the liquid crystalprojector apparatus of FIG. 1.

[0051]FIG. 7 is a view showing a simplified form of the structure of theliquid crystal projector apparatus.

[0052]FIG. 8 is a view showing an example of a driving control circuitused for the liquid crystal projector apparatus.

[0053]FIG. 9 is a view illustrating an example of a waveform variationat a portion of the circuit of FIG. 8.

[0054]FIGS. 10A to 10C are views illustrating meanings of gammacorrection in FIG. 8.

[0055]FIG. 11 is a view illustrating an example of a V-T (liquid crystaldrive voltage-transmissivity) characteristic of a liquid crystal panel.

[0056]FIG. 12 is a view illustrating an example of a temperature of aliquid crystal panel, a temperature in a housing and temperaturedetection data by a temperature sensor.

[0057]FIG. 13 is a view illustrating a relationship of the temperatureof a liquid crystal panel to an offset shift voltage of the liquidcrystal panel.

[0058]FIGS. 14A to 14B are views illustrating an example of arelationship of the time after power supply starting to the startingtime shift temperatures of liquid crystal panels for red, green andblue.

[0059]FIG. 15 is a view illustrating an example of a variation of theluminance in a case wherein the drive voltage for a liquid crystal panelis corrected, another case wherein the drive voltage is not correctedand a further case wherein the power supply is re-started.

[0060]FIG. 16 is a view simply illustrating a driving method for aliquid crystal projector apparatus of the present invention.

[0061]FIG. 17 is a view showing another embodiment of a driving controlcircuit for a liquid crystal projector apparatus of the presentinvention.

[0062]FIG. 18 is a view illustrating an example of a V-T characteristicof a liquid crystal panel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0063] In the following, preferred embodiments of the present inventionare described in detail with reference to the accompanying drawings.

[0064] It is to be noted that, since the embodiments described below arepreferred particular examples of the present invention, varioustechnically preferable limitations are applied to the embodiments, butthe scope of the present invention is not limited to the embodimentsunless it is recited in the following description that the presentinvention should be limited.

[0065]FIG. 1 is a perspective view showing an appearance of a preferredembodiment of a liquid crystal projector apparatus of the presentinvention.

[0066] Referring to FIG. 1, a liquid crystal projector apparatus 100 iscalled rear projector and has a housing 101. A mirror 102, an opticalunit 104 and so forth are built in the housing 101.

[0067] The housing 101 has an upper portion 105 and a lower portion 103,and a screen 106 is provided on the front side of the upper portion 105.A color image projected by the optical unit 104 is reflected by themirror 102 and can be projected in an enlarged scale to the rear faceside (inner face side) of the screen 106 of a front face portion 107.The liquid crystal projector apparatus 100 is a color liquid crystalprojector apparatus of the so-called three-plate type which uses threeliquid crystal panels.

[0068]FIG. 2 shows an example of an internal structure of the liquidcrystal projector apparatus 100 when the liquid crystal projectorapparatus 100 of FIG. 1 is viewed from the E side.

[0069] The upper portion 105 of the housing 101 has the screen 106. Apair of circuit boards 108 and 109, the optical unit 104 and so forthare built in the lower portion 103. The optical unit 104 is positionedsubstantially center of the lower portion 103, and the circuit boards108 and 109 are disposed on the right side and the left side of theoptical unit 104. A fan 3 for cooling a light source and so forth isprovided in the proximity of a light source 2 such as a lamp of theoptical unit 104. The cooling fan 3 is rotated to radiate heat generatedby the light source 2 to the outside.

[0070]FIG. 3 illustrates a manner wherein the fan 3 cools the lightsource 2.

[0071] When the fan 3 rotates, external air is introduced in a directionR1 into the housing 101 through an opening 111 of the housing 101, andthe air is guided in a direction of R2 along a guide duct 110 to coolthe light source 2. The air after the cooling is discharged along adirection R3 to the outside of the housing 101 through a duct 112.

[0072] In this manner, the cooling path for the light source 2 shown inFIG. 3 is a region sectioned by a wall 114 so as to be separate from theother space 141 of the housing 101.

[0073]FIG. 4 shows the optical unit 104 provided in the liquid crystalprojector apparatus 100 of FIG. 1.

[0074] The light source 2 and an optical block 130 are disposed on abase plate 131 provided in a housing of the optical unit 104. Theoptical block 130 includes an optical block case 132, a lid 134 forclosing the top of the optical block case 132, an upper cover 135, alower cover 136, and a circuit board 408. Optical parts are accommodatedin the optical block 130 as shown in FIG. 5.

[0075] The optical block 130 includes, for example, such optical partsas shown in FIG. 5. A pair of lens arrays 24 a and 24 b are disposedadjacent the light source 2, and a pair of dichroic mirrors 27 a and 27b and reflecting mirrors 28 a, 28 b and 28 c for separating light fromthe light source 2 into lights of red, green and blue are disposed alongan OL.

[0076] The dichroic mirrors 27 a and 27 b and the reflecting mirrors 28a, 28 b and 28 c serve as separating optical means of light of the lightsource 2. Along paths along which the separated lights of the threecolors pass, condensers 29 a, 29 b and 29 c, polarizing plates 30 a, 30b and 30 c, and liquid crystal panels 200, 201 and 202 which serve asoptical modulation means are disposed such that the lights of the threecolors may be introduced separately into different faces of a combiningprism 5 serving as combining optical means. A projection lens 32 forprojecting the combined light in an enlarged scale is provided in thefollowing stage of the combining prism 5.

[0077] Here, operation of the optical block 130 is described.

[0078] Illuminating light from the light source 2 such as a metal halidelamp passes through a cut filter 23 which intercepts ultraviolet raysand infrared rays, and enters the optical block 130.

[0079] The illuminating light entering the optical block 130 passesthrough the lens arrays 24 a and 24 b, and red light R of theilluminating light is separated and reflected by the dichroic mirror 27a. The separated red light R is reflected by the reflecting mirror 28 a,passes through the condenser 29 a and the polarizing plate 30 a, andthen passes through the liquid crystal panel 200 for red.

[0080] The illuminating light having passed through the dichroic mirrors27 a, that is, green light G and blue light B, the green light G isseparated and reflected by the dichroic mirror 27 b. The separated greenlight G passes through the condenser 29 b and the polarizing plates 30 band then passes through the liquid crystal panel 201 for green.

[0081] The blue light B having passed through the dichroic mirror 27 bpasses through a lens 31 a, is reflected by the reflecting mirror 28 b,and then passes through another lens 31 b and is reflected by thereflecting mirror 28 c, whereafter it passes through the condenser 29 cand the polarizing plate 30 c and then passes through the liquid crystalpanel 202 for blue.

[0082] The liquid crystal panels 200, 201 and 202 are driven by drivecircuits based on video input signals of red, green and blue andoptically modulate the red light, green light and blue right,respectively. Thereafter, the lights having passed through the liquidcrystal panels 200, 201 and 202 for the three colors are combined by thecombining prism 5 and projected in color in an enlarged scale on thescreen 106 of FIG. 1 by the projection lens 32. A color image isdisplayed on the screen by the optical block 130 in this manner.

[0083]FIG. 6 shows an example of an internal structure of the housing101. The optical unit 104 described above is disposed in the lowerportion 103 of the housing 101. When a cooling fan 140 rotates, the airis circulated in the direction indicated by arrow marks A1, A2, A3 andA4 in the space 141 in the housing 101.

[0084] The circulation of the air cools the liquid crystal panels 200,201 and 202 of the optical unit 104 shown in FIG. 5 such that theinternal air in the space 141 is circulated without taking in air fromthe outside of the housing 101 in order to prevent dust and so forthfrom being taken into the housing 101 from the outside. The space 141 isformed as a section separate from such a space for cooling the lightsource 2 as shown in FIG. 3.

[0085] Light L projected from the projection lens 32 shown in FIG. 6 isreflected by the mirror 102 as indicated by alternate long and shortdash lines and is projected in an enlarged scale on the inner face sideof the screen 106. The air in the space 141 is circulated such that itpasses the inside of the optical unit 104 and the inside of the screen106 and inside of the mirror 102 and then passes an air circulation path147.

[0086]FIG. 7 is a simplified figure of an example of an internalstructure of the liquid crystal projector apparatus 100 of FIG. 1. InFIG. 7, the light source 2, the optical unit 104 which is anilluminating optical system, the three liquid crystal panels 200, 201and 202, the projection lens 32, the screen 106 and so forth are shown,and the elements mentioned are accommodated in the housing 101.

[0087]FIG. 8 shows an example of a configuration of a driving controlcircuit 300 for driving the liquid crystal panels 200, 201 and 202.

[0088] The driving control circuit 300 generally includes an inputsignal generation section 301, three digital gamma correction sections302, 303 and 304, three D/A converters (digital/analog converters) 310,311 and 312, a first liquid crystal drive section 321, a second liquidcrystal drive section 322, a third liquid crystal drive section 323, aCPU (central processing unit) 403 serving as arithmetic operation means,a memory 404, and a single temperature sensor 405.

[0089] From the input signal generation section 301, an input signal SRfor red, an input signal SG for green and an input signal SB for blueare outputted. The input signal SR for red is inputted to the digitalgamma correction section 302. Similarly, the input signal SG for greenis inputted to the digital gamma correction section 303, and the inputsignal SB for blue is inputted to the digital gamma correction section304.

[0090] A gain adjustment section 302A and an offset adjustment section302B are connected to the digital gamma correction section 302.Similarly, a gain adjustment section 303A and an offset adjustmentsection 303B are connected to the digital gamma correction section 303,and a gain adjustment section 304A and an offset adjustment section 304Bare connected to the digital gamma correction section 304.

[0091] The digital gamma correction sections 302, 303 and 304 are partsfor digitally gamma correcting the corresponding input signal SR forred, input signal SG for green and input signal SB for blue,respectively.

[0092] The input signals SR, SG and SB have such a stepwise input signalwaveform as shown in (A) of FIG. 9. The waveform of the input signalsSR, SG and SB is changed into such a gamma output waveform 400 as shownin (B) of FIG. 9 by gamma correction by the digital gamma correctionsections 302, 303 and 304. The gamma output waveform 400 has an offset Fand a gain Ga set therein by operation of a gain adjustment section andan offset adjustment section. The digital gamma correction sections 302,303 and 304 gamma correct the input signals SR, SG and SB from thefollowing reason.

[0093]FIG. 10 illustrates the meaning of gamma correction simply.

[0094] For example, if a camera 1000 on the television station sideshown in FIG. 10A picks up an image of an image pickup object 1001, thenthe relationship between the camera signal and the brightness of theimage pickup object can be represented by a straight line D. And, aprocessing section 1002 transmits the television signal as abroadcasting wave in such a state that it has a characteristicrepresented by a curve D1 between the brightness of the image pickupobject and the television signal.

[0095] Meanwhile, a processing section 1004 of a cathode ray tube 1003side of the user side receives the broadcasting wave as seen in FIG.10B. The relationship between the brightness of the cathode ray tube1003 and a drive signal for the cathode ray tube 1003 is such a reversecharacteristic as represented by a curve D2 to the curve D1, and as aresult, the processing section 1004 can modify the relationship betweenthe brightness of the cathode ray tube 1003 and the brightness of theimage pickup object so as to be such as represented by a straight lineD3 to play back an image.

[0096] However, when it is tried to use the liquid crystal projectorapparatus 100 to play back the broadcasting wave from the processingsection 1002 side of the broadcasting side as seen in FIG. 10C, thedriving control circuit 300 must perform signal conversion differentfrom that of the cathode ray tube 1003 in accordance with acharacteristic unique to the liquid crystal panels 200, 201 and 202.

[0097] Since the liquid crystal panels 200, 201 and 202 have a peculiarcharacteristic indicated by a curve D4 called V-T characteristic, if thecharacteristic is not corrected but an image is displayed with a linearcharacteristic on the liquid crystal panels 200, 201 and 202, then aresulting image suffers from stopping of white at a portion thereof atwhich the transmissivity is high while stopping of black occurs atanother portion at which the transmissivity is low.

[0098] Therefore, it is necessary to use the digital gamma correctionsections 302, 303 and 304 shown in FIGS. 8 and 9 to perform correctionof the driving voltage-luminance characteristic (transmissivity) (V-Tcharacteristic) for the liquid crystal panels 200, 201 and 202,respectively.

[0099] The input signals corrected by the digital gamma correctionsections 302, 303 and 304 of FIG. 8 in this manner have a gamma outputwaveform 400 and are inputted to D/A converters 310, 311 and 312,respectively. A gain adjustment waveform 401 whose gain Gal is adjustedas seen in (C) of FIG. 9 is generated by each of the D/A converters 310,311 and 312.

[0100] The input signals with the gains adjusted after they are gammacorrected in this manner have the gain adjustment waveform 401 and aresupplied to the first liquid crystal drive section 321, second liquidcrystal drive section 322 and third liquid crystal drive section 323,respectively.

[0101] It is to be noted that, since general adjustment of thebrightness where the cathode ray tube 1003 is used as shown in FIG. 10is performed prior to the digital gamma correction sections shown inFIG. 8, non-linear conversion is performed by the digital gammacorrection sections. Consequently, by the brightness adjustment(adjustment of the V-T characteristic in the direction of the axis ofordinate), the shift of the curve D4 of the V-T characteristic by thetemperature cannot be corrected.

[0102] Further, each of the liquid crystal panels uses not driving witha dc voltage but reversed driving as seen from an offset shift waveform402 shown in (D) of FIG. 9 in order to prevent the image persistence andso forth of the liquid crystal. Therefore, a shift of a curve of the V-Tcharacteristic to a liquid crystal panel corresponds to an offset FT ofthe offset shift waveform 402 of (D) of FIG. 9. The shift of the offsetFT is a shift with respect to a common voltage VCOM. In short, in orderto correct the shift of the curve of the V-T characteristic, the valuesof the driving voltage to be applied to the liquid crystal panels 200,201 and 202 must be corrected in response to the temperatures of theliquid crystal panels 200, 201 and 202 after correction by the digitalgamma correction sections.

[0103] Referring back to FIG. 8, the first liquid crystal drive section321 includes a liquid crystal drive circuit 321A and an offsetadjustment section 321B. The offset adjustment section 321B is a partfor performing adjustment of an offset, that is, correction, of a drivevoltage VR generated by the liquid crystal drive circuit 321A.

[0104] Also the second liquid crystal drive section 322 similarlyincludes a liquid crystal drive circuit 322A and an offset adjustmentsection 322B. The offset adjustment section 322B is provided to performadjustment of an offset, that is, correction, of a drive voltage VGgenerated by the liquid crystal drive circuit 322A.

[0105] The third liquid crystal drive section 323 includes a liquidcrystal drive circuit 323A and an offset adjustment section 323B. Theoffset adjustment section 323B is provided to perform adjustment of anoffset, that is, correction, of a drive voltage VB generated by theliquid crystal drive circuit 323A.

[0106] The temperature sensor 405 shown in FIG. 8 is connected to theCPU 403 serving as arithmetic operation means. Also the memory 404 isconnected to the CPU 403. The CPU 403 includes a timer 403T.

[0107] The timer 403T is provided to count the time after power supplystarting at which a power supply 500 is started till steady operationentering.

[0108] The temperature sensor 405 shown in FIG. 8 is characterized inthat it is disposed at a location in the housing other than the liquidcrystal panels in the liquid crystal projector apparatus. Thetemperature sensor 405 is disposed, for example, on the circuit board408 of the optical unit 104 which is a location other than the liquidcrystal panels 200, 201 and 202. The circuit board 408 is shown also inFIG. 4.

[0109] Since the temperature sensor 405 is not disposed directly on theliquid crystal panels 200, 201 or 202 and it is neither necessary todispose the temperature sensor on a small liquid crystal panel nornecessary to dispose the temperature sensor at a portion exposed tolight, it is easy to mount from the structure.

[0110] The temperature sensor 405 detects the temperature in the housingof the liquid crystal projector apparatus on the circuit board 408.Temperature detection data TD detected by the temperature sensor 405 isinputted to the CPU 403. The CPU 403 stores the temperature detectiondata TD into the memory 404, for example, within a period of time afterpower supply starting till steady operation entering.

[0111] The CPU 403 serving as arithmetic operation means estimates thetemperatures of the liquid crystal panels based on the temperaturedetection data stored in the memory 404 to indirectly obtain actualtemperatures of the liquid crystal panels.

[0112] Since the temperature sensor 405 is not disposed directly on theliquid crystal panel 200, 201 or 202 but is disposed on the circuitboard 408 spaced away from the liquid crystal panels in this manner, thetemperature sensor 405 does not directly measure the temperature of theliquid crystal panels.

[0113] Accordingly, in order to estimate the temperatures of the liquidcrystal panels to indirectly obtain them, the CPU 403 arithmeticallyoperates in accordance with the following expression (1) to obtain thetemperatures of the liquid crystal panels.

Temperature of liquid crystal panel=indication temperature oftemperature sensor+starting time shift temperature  (1)

[0114]FIG. 11 illustrates examples of the V-T characteristic of a liquidcrystal panel.

[0115] Referring to FIG. 11, the axis of ordinate indicates thetransmissivity (called also as luminance characteristic) of the liquidcrystal panel, and the axis of abscissa indicates the driving voltage(applied voltage) for the liquid crystal panel.

[0116] In the V-T characteristic, a temperature curve J represents a V-Tcharacteristic where the temperature of the liquid crystal panel is26.5° C. Another temperature curve J1 represents a V-T characteristicwhere the temperature of the liquid crystal panel is 48.6° C. A furthertemperature curve J2 represents a ratio between the V-T characteristicswhere the temperature of the liquid crystal panel is 48.6°/26.5° C.

[0117] Usually, in a cathode ray tube or the like, brightness adjustmentof an image is performed by varying the amplitude of an input signal ofFIG. 9. This is because the system is such that a variation of theapplied voltage appears directly as a variation of the brightness fromthe characteristic of FIG. 10B.

[0118] In contrast, in a liquid crystal panel, since it has the V-Tcharacteristic illustrated in FIG. 11, a linear variation of the appliedvoltage appears as a non-linear variation of the brightness, theadjustment shown in (B) of FIG. 9 is performed to correct the V-Tcharacteristic in FIG. 10. And therefore, the method of the brightnessadjustment used in a system of a cathode ray tube and so forth, that is,the method of varying the amplitude of an input signal, cannot be usedto cancel the shift of the V-T characteristic by the temperature of FIG.11. In other words, the shift of the V-T characteristic can be correctedonly at the section of (D) of FIG. 9 after the V-T characteristiccorrection of FIG. 9.

[0119]FIG. 12 illustrates variations of the temperature detection dataTD detected by the temperature sensor 405 of FIG. 8, the actualtemperature T1 of a liquid crystal panel and the temperature T2 in thehousing within a time from the power supply starting time t1 at whichthe power supply is started to the time t2.

[0120] At the power supply starting time t1, the temperature detectiondata TD, the temperature T1 of the liquid crystal panel and thetemperature T2 in the housing are, for example, all 25° C. near to aroom temperature.

[0121] As the time elapses from the power supply starting time t1 to thesteady operation entering time t2, the temperature T1 of the liquidcrystal panel rises suddenly when compared with the temperature T2 inthe housing and the temperature detection data TD. Thereafter, thetemperature T1 of the liquid crystal panel rises moderatelysubstantially in parallel to the temperature T2 in the housing and thetemperature detection data TD, and the temperature T1 of the liquidcrystal panel reaches 50° C. at the steady operation entering time t2.The temperature T2 in the housing is approximately 35° C. at the steadyoperation entering time t2, and the temperature detection data TD isapproximately 30° C.

[0122]FIG. 13 illustrates an example of an estimation arithmeticoperation process of the temperature of a liquid crystal panel given asthe expression (1) above.

[0123] An offset shift voltage AV of the liquid crystal panel isindicated by the axis of ordinate, and the temperature of the liquidcrystal panel to be estimated is indicated by the axis of abscissa.

[0124] The offset shift voltage AV of the liquid crystal panel of theaxis of ordinate represents data for shifting the driving voltage forthe liquid crystal of the axis of abscissa of the V-T characteristic ofFIG. 11 along the axis of abscissa. The offset shift voltage AV of theliquid crystal panel is, in the first liquid crystal drive section 321of FIG. 8, an offset shift voltage AV to be supplied from the offsetadjustment section 321B to the liquid crystal drive circuit 321A. Thissimilarly applies to the second liquid crystal drive section 322 andalso the third liquid crystal drive section 323. In particular, theoffset adjustment section 322B supplies another offset shift voltage AVto the liquid crystal drive circuit 322A. The offset adjustment section323B supplies a further offset shift voltage AV to the liquid crystaldrive circuit 323A.

[0125] Referring back to FIG. 13, if the value of the offset shiftvoltage AV of the axis of ordinate is shifted in the positive direction,then the brightness of the liquid crystal panel decreases, but if thevalue of the offset shift voltage AV is shifted in the negativedirection, then the brightness of the liquid crystal panel increases.

[0126] It is indicated by the expression 1 given hereinabove that thetemperature of a liquid crystal panel is the sum of the indicationtemperature (temperature detection data TD) of the temperature sensorand a starting time shift temperature TS.

[0127] The starting time shift temperature TS can be obtained in amanner illustrated in FIGS. 14. FIG. 14A indicates a relationship of thetime from the power supply starting time to the starting time shifttemperature of the liquid crystal panel for red. FIG. 14B indicates arelationship of the time from the power supply starting time to thestarting time shift temperature of the liquid crystal panel for green.FIG. 14C indicates a relationship of the time from the power supplystarting time to the starting time shift temperature of the liquidcrystal panel for blue.

[0128] Data of FIG. 14A, FIG. 14B and FIG. 14C represent data of thestarting time shift temperature TS, respectively. The data of thestarting time shift temperature TS is obtained, for each of the liquidcrystal panels, by plotting the difference K between the temperature T1and the temperature detection data TD of the liquid crystal panel of theexample illustrated in FIG. 12 from the power supply starting time t1 tothe steady operation entering time t2.

[0129] Whereas the starting time shift temperature of the liquid crystalpanel for red is 5 C at the power supply starting time t1 as seen inFIG. 14A, the starting time shift temperature at the steady operationentering time is 15° C. Whereas the starting time shift temperature ofthe liquid crystal panel for green is 5° C. at the power supply startingtime t1 as seen in FIG. 14B, the starting time shift temperature at thesteady operation entering time is 20° C. Whereas the starting time shifttemperature of the liquid crystal panel for blue is 5° C. at the powersupply starting time t1 as seen in FIG. 14C, the starting time shifttemperature at the steady operation entering time is 25° C.

[0130] In this manner, the temperature at the steady operation enteringtime is a little different among the different liquid crystal panels.Based on the starting time shift temperatures TS of the liquid crystalpanels for the different colors, the temperatures of the liquid crystalpanels are estimated as seen in FIG. 13 using the expression (1).

[0131] Now, a driving method for the liquid crystal projector apparatusdescribed above is described with reference to FIG. 16.

[0132] First in a temperature detection step ST1, the temperature sensor405 of FIG. 8 detects the temperature, for example, of the circuit board408 which is a location other than the liquid crystal panels in thehousing 101 of the liquid crystal projector apparatus 100 shown in FIG.1.

[0133] The temperature sensor 405 supplies the temperature detectiondata TD to the CPU as seen in FIG. 8. The CPU 403 can obtain thetemperature detection data TD from the temperature sensor 405 for aperiod of time after the power supply starting time of the power supply500 till a steady operation entering time. The above period of time isdetermined by the timer 403T. The temperature detection data TD obtainedin this manner, which supplied from the CPU is stored in the memory 404.

[0134] The temperature detection data TD of the temperature sensor 405corresponds to the indication temperature of the temperature sensorillustrated in FIG. 13. The CPU 403 serving as arithmetic operationmeans arithmetically operates and estimates the temperatures of theliquid crystal panels as seen in FIG. 13 in an arithmetic operation stepST2 of FIG. 16. In particular, the temperature of each liquid crystalpanel is obtained by adding the starting time shift temperature TS tothe temperature detection data TD which is the indication temperature ofthe temperature sensor. However, the starting time shift temperature ofthe liquid crystal panel for red illustrated in FIG. 14A, the startingtime shift temperature of the liquid crystal panel for green illustratedin FIG. 14B and the starting time shift temperature of the liquidcrystal panel for blue illustrated in FIG. 14C have different valuesfrom one another.

[0135] As seen in FIG. 13, the temperature of a liquid crystal panel forwhich estimation is to be performed is represented by the axis ofabscissa, and the offset shift voltage AV of the liquid crystal panel isrepresented by the axis of ordinate. The relationship between the offsetshift voltage AV and the temperature of the liquid crystal panel can berepresented linearly by a characteristic line M. The offset shiftvoltages AV of the liquid crystal panels are adjusted in response to thetemperatures of the liquid crystal panels for the different colors.

[0136] Thus, in a drive voltage supplying step ST3 of FIG. 16, a controlamount for the offset shift voltage AV illustrated in FIG. 13 for theliquid crystal panel 200 for read is provided to the offset adjustmentsection 321B of the first liquid crystal drive section 321 of FIG. 8 inaccordance with an instruction from the CPU 403.

[0137] Similarly, another control amount is provided from the CPU 403 tothe offset adjustment section 322B of the second liquid crystal drivesection 322. To the offset adjustment section 323B of the third liquidcrystal drive section 323, a further control amount is provided from theCPU 403.

[0138] Consequently, an offset shift voltage AV is provided from theoffset adjustment section 321B to the liquid crystal drive circuit 321A,and another offset shift voltage AV is supplied from the offsetadjustment section 322B to the liquid crystal drive circuit 322A while afurther offset shift voltage AV is supplied from the offset adjustmentsection 323B to the liquid crystal drive circuit 323A.

[0139] As a result, a drive voltage VR corrected with the offset shiftvoltage AV is supplied from the liquid crystal drive circuit 321A to theliquid crystal panel 200 for red. To the liquid crystal panel 201 forgreen, another drive voltage VG corrected with the offset shift voltageAV is supplied from the liquid crystal drive circuit 322A. To the liquidcrystal panel 202 for blue, a further drive voltage VB corrected withthe offset shift voltage AV is supplied from the liquid crystal drivecircuit 323A. The offset shift voltages AV supplied from the offsetadjustment section 321B, offset adjustment section 322B and offsetadjustment section 323B have different values from one another becausethe values of the start time shift temperature of the liquid crystalpanels 200, 201 and 202 are different from one another as seen from FIG.14A, FIG. 14B and FIG. 14C.

[0140] In FIG. 15, the axis of ordinate indicates the luminance of aliquid crystal panel, and the axis of abscissa indicates the elapsedtime from the power supply starting time t1.

[0141] A curve E1 indicates an example of a variation of the luminanceof the liquid crystal panel when the drive voltage is corrected in theembodiment of the present invention. Another curve E2 indicates acomparative example which is an example wherein correction of the drivevoltage for the liquid crystal panel is not performed. Where correctionis performed, the luminance exhibits a fixed value substantially stablyafter the power supply starting time t1 till the steady operationentering time as seen from the curve E1. In contrast, from the curve E2in the case wherein no correction is performed for the starting voltage,it can be seen that the luminance drops suddenly after the power supplystarting time t1.

[0142] In a liquid crystal projector apparatus, the stability of theluminance is very significant to the picture quality of a display imagebecause there is no pushup of a peak.

[0143] As seen from the curve E2, where no correction is performed, theluminance decreases, for example, by approximately 20%. This is a resultof the shifting of the V-T characteristic by a temperature variation.

[0144] Although it is possible to perform adjustment with the brightnessafter 30 minutes by simply shifting the VT characteristic by a luminancedrop for a time of, for example, approximately 30 minutes after thepower supplying starting time, in this instance, the luminance increasesby approximately 20% conversely within the time of 30 minutes. Besides,since the apparatus in question is a liquid crystal projector apparatus,the luminance of the white does not increase any more, and stopping ofwhite occurs within the period of 30 minutes. Further, it is a matter ofcourse that, since the drive voltage for a liquid crystal panel iscorrected with an estimated temperature of the liquid crystal panel,also it is possible to cope with a temperature variation by a variationof the environment.

[0145]FIG. 17 shows another embodiment of the present invention.

[0146] A driving control circuit 300 of FIG. 17 is substantially similarto the driving control circuit 300 of FIG. 8, but includes, in additionto the temperature sensor 405, an additional room temperature detectionsensor 1100.

[0147] The additional room temperature detection sensor 1100 isdisposed, for example, on an outer face of the housing 101 shown in FIG.1 and can detect a room temperature of a room in which the liquidcrystal projector apparatus 100 is placed.

[0148] After the power supply for the liquid crystal projector apparatusis started and the temperature of the liquid crystal panels rises, thepower supply may be stopped once and then re-started. When the powersupply is re-started in this manner, if correction of the drivingvoltages for the liquid crystal panels is performed based on the periodof time from the starting time, then so-called counter correction takesplace. It is to be noted that, in this instance, since the countercorrection acts in a direction to lower the luminance, merely a displayimage becomes darker, and the stopping of white which matters upon thepower supply starting does not occur.

[0149] In order to prevent such counter correction which makes a displayimage darker, the room temperature detection sensor 1100 for detecting aroom temperature shown in FIG. 17 is provided separately from thetemperature sensor 405. A state wherein the power supply for the liquidcrystal projector apparatus is started once and then stopped once andthereafter started again, that is, whether re-starting of the powersupply is performed, is discriminated based on the difference betweenroom temperature data RD by the room temperature detection sensor 1100and the temperature detection data TD of the temperature sensor 405 inthe housing.

[0150] A curve E3 of FIG. 15 indicates an example of a variation of theluminance when re-starting is performed, and it can be seen that, whenthe power supply is restarted, the luminance drops considerably. Sincethe CPU 403 arithmetically operates and processes the difference betweenthe temperature detection data TD of the temperature sensor 405 and theroom temperature data RD of the room temperature detection sensor todiscriminate whether or not re-starting is performed, the CPU 403 candiscriminate whether or not the power supply is restarted and canperform such determination that, when the power supply is re-started, itchanges the correction values for the drive voltage based on the timeafter the re-starting time or it does not perform such correction.

[0151] It is to be noted that, in the control of the drive voltages tobe applied to the liquid crystal panels, dc components of the drivevoltages VR, VG and VB to be applied to the liquid crystal panels 200,201 and 202 shown in FIG. 8 are controlled and corrected.

[0152] As described hereinabove, a number of liquid crystal projectorapparatus use three liquid crystal panels to form three colors of red,green and blue, and in many cases, the temperatures of the three liquidcrystal panels are different from one another as seen from FIG. 14A,FIG. 14B and FIG. 14C from a difference in light energy. In this case,three liquid crystal panels include the correction values based on thedifference in the temperature among three colors, respectively, so thatit is possible to perform optimum correction for three liquid crystalpanels. Where the temperature difference among the three liquid crystalpanels is great, the white balance is disordered, and this can be copedwith by providing different correction values for them.

[0153] Where the starting time shift temperature is used as a separateparameter as in the expression 1 given hereinabove, a panel temperaturenecessary for temperature correction can be determined from atemperature variation in the housing without directly measuring thetemperature of the liquid crystal panel. This is effective where thetemperatures of the liquid crystal panels are different from thetemperature of the temperature sensor with a liquid crystal projectorapparatus wherein internal circulation is used for the liquid crystalpanels because the temperature shift by the starting time is great.

[0154] In the embodiments of the present invention, the picture qualitycan be corrected so that picture quality deterioration of white stoppingor dark stopping may not occur depending upon a variation of the ambienttemperature of the liquid crystal projector apparatus without directlymeasuring the temperature of the liquid crystal panels of the liquidcrystal projector apparatus.

[0155] Where an air circulating system in the housing is used as acooling system for the liquid crystal panels, even with a liquid crystalprojector apparatus wherein the temperature variation of the liquidcrystal panels cannot be measured directly, such correction as in thecase wherein the temperature is measured directly can be performed bycorrecting the drive voltages depending upon the time after the powersupply starting time.

[0156] Where not brightness correction by a shift of the V-Tcharacteristic in the direction of the axis of ordinate by a temperaturevariation of a liquid crystal panel but offset shifting of a liquidcrystal drive circuit is used for correction, correction can beperformed without varying the gradation property.

[0157] Where two temperature sensors are used, also counter correctionupon re-starting can be prevented, and optimum correction can beanticipated.

[0158] Since a countermeasure against white stopping and dark stoppingwhich occur with a liquid crystal panel from a variation of the ambienttemperature can be taken, the dynamic range for utilization of lightafter the adjustment can be expanded to improve the picture quality.

[0159] Where no temperature correction is involved, since an image isrepresented using the inside of the dynamic range of the liquid crystalpanel within which white stopping or dark stopping by a temperaturevariation does not occur, the luminance and the contrast during use arelowered.

[0160] Where correction values for the drive voltage to be applied tothe three liquid crystal panels for red, green and blue are providedindependently of each other, also a variation in white balance caused bya temperature variation where a temperature difference is presentbetween the liquid crystal panels for different colors can be corrected.

[0161] In the liquid crystal projector, temperature data in theapparatus is detected and differences from a temperature variationdepending upon time of the liquid crystal panels upon starting areprovided as data, and a drive voltage shift depending upon thetemperature of the liquid crystal is controlled based on the differencewith a calculated value to prevent white stopping and dark stopping.

[0162] By the way, the present invention is not limited to theembodiments described above.

[0163] In the embodiments described above, a liquid crystal projectorapparatus for so-called color display is taken as an example. However,in a liquid crystal projector not for color display but forblack-and-white display, not three liquid crystal panels but a singleliquid crystal panel may be used. Further, the present invention can beapplied also to a liquid crystal projector apparatus wherein a screen isnot provided on a housing but an image is projected onto a screenprovided at a different position spaced from the housing.

[0164] While the preferred embodiments of the present invention havebeen described using the specific terms, such description is forillustrative purposes only, and it is to be understood that changes andvariations may be made without departing from the spirit or scope of thefollowing claims.

What is claimed is:
 1. A liquid crystal projector apparatus whichincludes a liquid crystal panel for optically modulating light from alight source with an input signal and projects the optically modulatedlight from said liquid crystal panel to display an image, characterizedin that it comprises a temperature sensor for detecting a temperature ata location in said liquid crystal projector apparatus except said liquidcrystal panel, a memory for storing temperature detection data obtainedby said temperature sensor within a period from a power supply startingtime to a steady operation entering time of said liquid crystalprojector apparatus, arithmetic operation means for estimating atemperature of said liquid crystal panel based on the temperaturedetection data stored in said memory to indirectly obtain thetemperature of said liquid crystal panel, and a liquid crystal drivesection for correcting a drive voltage for driving said liquid crystalpanel with an output signal of said arithmetic operation means andapplying the corrected drive voltage to said liquid crystal panel.
 2. Aliquid crystal projector apparatus according to claim 1, wherein saidliquid crystal drive section controls a dc component of the drivevoltage to be applied to said liquid crystal panel to correct thevoltage.
 3. A liquid crystal projector apparatus according to claim 2,wherein said light source and said liquid crystal panel are disposed ina housing, and said liquid crystal projector apparatus further comprisescooling means for circulating air in said housing without taking inexternal air to cool said liquid crystal panel in said housing.
 4. Aliquid crystal projector apparatus according to claim 3, wherein saidliquid crystal panel includes a liquid crystal panel for red, a liquidcrystal panel for green and a liquid crystal panel for blue, and saidliquid crystal drive section includes a first liquid crystal drivesection for correcting a drive voltage for driving said liquid crystalpanel for red with an output signal of said arithmetic operation meansand applying the corrected drive voltage to said liquid crystal panelfor red, a second liquid crystal drive section for correcting a drivevoltage for driving said liquid crystal panel for green with anotheroutput signal of said arithmetic operation means and applying thecorrected drive voltage to said liquid crystal panel for green, and athird liquid crystal drive section for correcting a drive voltage fordriving said liquid crystal panel for blue with a further output signalof said arithmetic operation means and applying the corrected drivevoltage to said liquid crystal panel for blue.
 5. A liquid crystalprojector apparatus according to claim 1, further comprising a roomtemperature detection sensor for detecting a room temperature separatelyfrom said temperature sensor, and wherein said arithmetic operationmeans arithmetically operates, at the power supply starting time, adifference between the temperature detection data of said temperaturesensor and room temperature detection data of said room temperaturedetection sensor.
 6. A driving method for a liquid crystal projectorapparatus which includes a liquid crystal panel for optically modulatinglight from a light source with an input signal and projects theoptically modulated light from said liquid crystal panel to display animage, characterized in that it comprises a temperature detection stepof detecting a temperature at a location in said liquid crystalprojector apparatus except said liquid crystal panel by means of atemperature detector, an arithmetic operation step of storingtemperature detection data obtained by said temperature sensor within aperiod from a power supply starting time to a steady operation enteringtime of said liquid crystal projector apparatus into a memory andestimating a temperature of said liquid crystal panel based on saidtemperature detection data stored in said memory to indirectly obtainthe temperature of said liquid crystal panel by means of arithmeticoperation means, and a drive voltage supplying step of correcting adrive voltage for driving said liquid crystal panel with an outputsignal of said arithmetic operation means by a liquid crystal drivesection and applying the corrected drive voltage to said liquid crystalpanel.
 7. A driving method for a liquid crystal projector apparatusaccording to claim 6, wherein said liquid crystal drive section controlsa dc component of the drive voltage to be applied to said liquid crystalpanel to correct the voltage.
 8. A driving method for a liquid crystalprojector apparatus according to claim 7, wherein said light source andsaid liquid crystal panel are disposed in a housing, and cooling meanscirculates air in said housing without taking in external air to coolsaid liquid crystal panel in said housing.
 9. A driving method for aliquid crystal projector apparatus according to claim 8, wherein saidliquid crystal panel includes a liquid crystal panel for red, a liquidcrystal panel for green and a liquid crystal panel for blue, and whereina first liquid crystal drive section corrects a drive voltage fordriving said liquid crystal panel for red with an output signal of saidarithmetic operation means and applies the corrected drive voltage tosaid liquid crystal panel for red, a second liquid crystal drive sectioncorrects a drive voltage for driving said liquid crystal panel for greenwith another output signal of said arithmetic operation means andapplies the corrected drive voltage to said liquid crystal panel forgreen, and a third liquid crystal drive section corrects a drive voltagefor driving said liquid crystal panel for blue with a further outputsignal of said arithmetic operation means and applies the correcteddrive voltage to said liquid crystal panel for blue.
 10. A drivingmethod for a liquid crystal projector apparatus according to claim 6,wherein said liquid crystal projector apparatus further comprises a roomtemperature detection sensor for detecting a room temperature separatelyfrom said temperature sensor, and said arithmetic operation meansarithmetically operates, at the power supply starting time, a differencebetween the temperature detection data of said temperature sensor androom temperature detection data of said room temperature detectionsensor.